“Sometimes I can’t believe it happened,” said Elen Feuerriegel as the 3D printer by her side chugs out a thermoplastic copy of the cranium of an ancient human.

“I’m doing something ordinary, something I do every day, and then remember that two years ago I was working 30 metres underground recovering the remains of Homo naledi, a previously unknown human species.”

Feuerriegel, a PhD student in palaeoanthropology at the Australian National University, was one of six excavators – dubbed underground astronauts by an excited media – who retrieved the bones of up to 15 individuals from a small and almost inaccessible cave.

Part of an expedition organised by Professor Lee Berger from the University of Witwatersrand to investigate the Rising Star Cave in South Africa, it was the task of the Feuerriegel and the other five excavators to reach a small and unmapped annex to the cave system called the Dinaledi Chamber.

“To get to the chamber meant worming our way through a fissure that in one place narrowed to just 18 centimetres,” Feuerriegel said. “The fissure itself was a 12-metre drop that ended in a tiny landing, followed by another four metre drop to the floor of the chamber.”

What Feuerriegel first saw there will stay with her for the rest of her life.

“It was a wonderful, exhilarating experience. It was incredible amount of fossil material in one place. It was almost impossible to move without stepping on a jaw or leg bone.

“As our eyes got used to the dimness and we became more experienced at discerning fossils in the floor sediment, new finds seemed to appear out of nowhere.”

Despite her interest in science starting as a young teenager, her appearance at the Rising Star Cave System was never a given. She reached palaeoanthropology through a route almost as torturous as the entrance to the Dinaledi Chamber.

“My first love was marine biology, particularly sharks. That somehow morphed into a fascination with volcanoes. Then my mum, an information architect, helped me put together a web page for a school project I did on human evolution.”

Feuerriegel speaks about evolution through natural selection with a focused passion.

“For me, evolution is the great leveler. We humans are as subject to evolutionary forces as other species.”

The American crime procedural CSI: Crime Scene Investigation also stirred in her an interest in anatomy.

She did her first degree in sociocultural anthropology at the University of Queensland. “I’d given up on the idea of palaeoanthropology until I did an intensive summer course on human evolution.”

With an honours degree in her pocket, Feuerriegel came to the ANU to do her masters, and in 2013 began her PhD in palaeoanthropology.

Later that year, Lee Berger put the call out for people with a special and unusual skill set.

“He wanted skinny palaeoanthropologists who were also experienced climbers or cavers.”

Feuerriegel, who enjoyed wall-climbing and hiking, and had previously worked in a mine shaft in Sima de las Palomas in Spain looking for the remains of Neanderthals, applied for one of the openings.

“Despite the specialist skill set, there were 60 applicants. I was one of six chosen.”

Within three weeks of an online interview, Feuerriegel found herself in South Africa retrieving the remains of a new human species, Homo naledi.

“We worked in two shifts, each with three excavators and two support cavers. Each shift lasted anywhere between three and six hours, depending on the task. The expedition tried to get at least two shifts down in the chamber every day, and sometimes three.

“For the first few days it could take up to an hour to get down from the surface to the chamber, but by the end of our stay there we’d reduced that to 20 minutes, giving us much more time for the real work.”

Towards the end of the work, seasonal rains raised the water table.

“There was no danger to us – the site was well above the water table – but conditions gradually got worse and surfaces more and more slippery.”

In the end, the excavators recovered the remains of 15 individuals, male and female, ranging in age from neonatal to an older female with very worn teeth.

Feuerriegel said she’s sure what the team discovered is a new species of ancient human.

“Morphologically, Homo naledi sits somewhere in the bridge between the latter Australopithecines and the early Homo, having features of both as well as some unique features all of its own. Exactly where it fits is something we don’t know yet.

“The other thing we don’t know at this point is how old the remains are. The bones we found had not yet been replaced with minerals like silica, but were still made up of hydroxylapatite, a form of calcium.”

She said if the remains proved to be between two and three million years old, H. naledi is the earliest definite example of Homo with skeletal material representing the whole body.

“If the remains are between one and two million years old, the date’s about right for a hominin of H.  naledi’s morphology.

“And if the date is less than one million years old, it means we have multiple species of hominins existing at the same time in South Africa. In that case, H. naledi’s small braincase and primitive morphology must make us seriously reconsider what it means to be a member of our own genus.”

Early reaction among some palaeoanthropologists hasn’t been all positive.

“Claims that the remains represent an early form of Homo erectus are fanciful,” Feuerriegel said. “A lot of critics have also focused on Lee’s description of the appearance of the bodies in one place as ‘ritual’.

“In this case, we aren’t suggesting anything spiritual, only that it represents repeated and deliberate behaviour.”

One of the career highlight for any palaeoanthropologist is to be one of the official ‘describers’ of a new species; thanks to her time in South Africa, Feuerriegel, at the age of 26 and still at least six months from finishing her PhD, is one of the names on the scientific paper officially naming the new species.

“I’ll also be lead author on a paper describing H. naledi’s upper limb, an area of morphology I’m particularly interested in.”

Feuerriegel said humans hold themselves on a pedestal as a species, above and apart from our ancestors.

“If there’s one thing H. naledi illustrates, it’s that the characteristics and behaviours we believe make us unique are not so unique after all.”